This application is based on Japanese Patent Applications Nos. 2000-200591 and 2000-368342 filed respectively on Jul. 3, 2000 and Dec. 4, 2000, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a taking lens device. More specifically, the present invention relates to a taking lens device that optically takes in an image of a subject through an optical system and that then outputs the image as an electric signal by means of an image sensor, for example a taking lens device that is used as a main component of a digital camera, a video camera, or a camera that is incorporated in or externally fitted to a device such as a digital video unit, a personal computer, a mobile computer, a portable telephone, or a personal digital assistant (PDA). The present invention relates particularly to a taking lens device provided with a compact zoom lens system.
2. Description of the Prior Art
In recent years, with the explosive spread of portable information terminals called PDAs and portable telephones, an increasing number of models have been coming to incorporate a compact digital camera or digital video unit employing a CCD (charge-coupled device) or CMOS (complementary metal-oxide semiconductor) sensor as an image sensor. When such a digital camera or the like is miniaturized using an image sensor with a relatively small effective image-sensing surface area, its optical system also needs to be miniaturized accordingly. As a compact zoom lens with a small number of lens elements for use in a digital camera or the like provided with an image sensor with a small effective area, Japanese Patent Application Laid-Open No. H1-183617 proposes a zoom lens of a so-called negative-positive two-unit type composed of, from the object side, a first lens unit having a negative optical power and a second lens unit having a positive optical power. Zoom lenses of this type include a minimum number of movable lens units and have simple mechanical structures, and are therefore suitable as low-cost zoom lenses. On the other hand, Japanese Patent Applications Laid-Open Nos. H5-164965, H 1-352397, H10-232349, and other applications propose zoom lenses of the same optical type that include fewer lens elements.
In the zoom lens proposed in Japanese Patent Application Laid-Open No. H1-183617 mentioned above, the second lens unit is composed of three lens elements, namely two positive lens elements and one negative lens element. This makes the optical axis length of the second lens unit too long to make the entire zoom lens satisfactorily compact. In the zoom lens proposed in the Japanese Patent Application Laid-Open No. H5-164965 mentioned above, the first and second lens units are each composed of one lens element; that is, the entire zoom lens includes only two lens elements, the least possible number theoretically. However, this zoom lens offers a zoom ratio lower than 2xc3x97 and a dark f-number. In the zoom lenses proposed in the Japanese Patent Applications Laid-Open Nos. H11-352397 and H10-232349 mentioned above, the first or second lens unit is stationary. This requires that an image sensor be moved to compensate for the defocusing resulting from zooming.
An object of the present invention is to provide a taking lens device provided with a zoom lens system that permits cost reduction and miniaturization to be achieved simultaneously and that offers a bright f-number and a zoom ratio of about 2xc3x97 to 3xc3x97.
To achieve the above object, according to one aspect of the present invention, a taking lens device is provided with: a zoom lens system, including a plurality of lens units, for forming an optical image of an object with variable magnification achieved by varying the distances between the lens units; and an image sensor for converting the optical image formed by the zoom lens system into an electric signal. Here, the zoom lens system includes, from the object side to the image side: a first lens unit that has a negative optical power, that is composed solely of a single negative lens element having a sharper curvature on the image side than on the object side thereof, and that is moved along the optical axis during zooming; and a second lens unit that is disposed with an aerial distance secured between itself and the first lens unit, that has a positive optical power, and that is moved along the optical axis during zooming. Moreover, the following conditional formulae (1) and (2) are fulfilled:
0.3 less than t1/Yxe2x80x2 less than 1.5xe2x80x83xe2x80x83(1) 
1.4 less than |f1/fw| less than 5xe2x80x83xe2x80x83(2) 
where
t1 represents the axial thickness (surface-to-surface distance along the optical axis) of the negative lens element constituting the first lens unit;
Yxe2x80x2 represents the maximum image height shootable;
f1 represents the focal length of the first lens unit; and
fw represents the focal length of the entire zoom lens system at the wide-angle end.
According to another aspect of the present invention, a taking lens device is provided with: a zoom lens system, including a plurality of lens units, for forming an optical image of an object with variable magnification achieved by varying the distances between the lens units; and an image sensor for converting the optical image formed by the zoom lens system into an electric signal. Here, the zoom lens system includes, from the object side to the image side: a first lens unit that has a negative optical power, that is composed solely of a single negative lens element having a sharper curvature on the image side than on the object side thereof, and that is moved along the optical axis during zooming; and a second lens unit that is disposed with an aerial distance secured between itself and the first lens unit, that has a positive optical power, that includes two lens elements, namely, from the object side, one positive lens element and one positive or negative lens element, and that is moved along the optical axis during zooming.
According to another aspect of the present invention, a taking lens device is provided with: a zoom lens system, including a plurality of lens units, for forming an optical image of an object with variable magnification achieved by varying the distances between the lens units; and an image sensor for converting the optical image formed by the zoom lens system into an electric signal. Here, the zoom lens system includes, from the object side to the image side: a first lens unit that has a negative optical power, that is composed solely of a single negative lens element made of resin and having a sharper curvature on the image side than on the object side thereof, and that is moved along the optical axis during zooming; and a second lens unit that is disposed with an aerial distance secured between itself and the first lens unit, that has a positive optical power, that has a lens element made of resin at the image-side end thereof, and that is moved along the optical axis during zooming.
According to another aspect of the present invention, a taking lens device is provided with: a zoom lens system, including a plurality of lens units, for forming an optical image of an object with variable magnification achieved by varying the distances between the lens units; and an image sensor for converting the optical image formed by the zoom lens system into an electric signal. Here, the zoom lens system includes, from the object side to an image side: a first lens unit that has a negative optical power, that is composed solely of a single negative lens element having a sharper curvature on the image side than on the object side thereof, and that is moved along the optical axis during zooming; and a second lens unit that is disposed with an aerial distance secured between itself and the first lens unit, that has a positive optical power, that is composed solely of a single positive lens element having a sharper curvature on the object side than on the image side thereof, and that is moved along the optical axis during zooming,